1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3 * Copyright (c) 2022-2024 Oracle. All Rights Reserved.
4 * Author: Darrick J. Wong <djwong@kernel.org>
5 */
6 #ifndef XFS_HOOKS_H_
7 #define XFS_HOOKS_H_
8
9 #ifdef CONFIG_XFS_LIVE_HOOKS
10 struct xfs_hooks {
11 struct blocking_notifier_head head;
12 };
13
14 /*
15 * If jump labels are enabled in Kconfig, the static key uses nop sleds and
16 * code patching to eliminate the overhead of taking the rwsem in
17 * blocking_notifier_call_chain when there are no hooks configured. If not,
18 * the static key per-call overhead is an atomic read. Most arches that can
19 * handle XFS also support jump labels.
20 *
21 * Note: Patching the kernel code requires taking the cpu hotplug lock. Other
22 * parts of the kernel allocate memory with that lock held, which means that
23 * XFS callers cannot hold any locks that might be used by memory reclaim or
24 * writeback when calling the static_branch_{inc,dec} functions.
25 */
26 # define DEFINE_STATIC_XFS_HOOK_SWITCH(name) \
27 static DEFINE_STATIC_KEY_FALSE(name)
28 # define xfs_hooks_switch_on(name) static_branch_inc(name)
29 # define xfs_hooks_switch_off(name) static_branch_dec(name)
30 # define xfs_hooks_switched_on(name) static_branch_unlikely(name)
31
32 struct xfs_hook {
33 /* This must come at the start of the structure. */
34 struct notifier_block nb;
35 };
36
37 typedef int (*xfs_hook_fn_t)(struct xfs_hook *hook, unsigned long action,
38 void *data);
39
40 void xfs_hooks_init(struct xfs_hooks *chain);
41 int xfs_hooks_add(struct xfs_hooks *chain, struct xfs_hook *hook);
42 void xfs_hooks_del(struct xfs_hooks *chain, struct xfs_hook *hook);
43 int xfs_hooks_call(struct xfs_hooks *chain, unsigned long action,
44 void *priv);
45
46 static inline void xfs_hook_setup(struct xfs_hook *hook, notifier_fn_t fn)
47 {
48 hook->nb.notifier_call = fn;
49 hook->nb.priority = 0;
50 }
51
52 #else
53
54 struct xfs_hooks { /* empty */ };
55
56 # define DEFINE_STATIC_XFS_HOOK_SWITCH(name)
57 # define xfs_hooks_switch_on(name) ((void)0)
58 # define xfs_hooks_switch_off(name) ((void)0)
59 # define xfs_hooks_switched_on(name) (false)
60
61 # define xfs_hooks_init(chain) ((void)0)
62 # define xfs_hooks_call(chain, val, priv) (NOTIFY_DONE)
63 #endif
64
65 #endif /* XFS_HOOKS_H_ */
66
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